This invention relates generally to electric resistance heating coils, and more particularly to a method and apparatus for forming lengths of coils of desired dimensions and resistance and transferring the formed coils to a first folding station. During manufacture, electrical resistance space heating assemblies of the type employing a coiled resistance element require various forming, moving, manipulating, and checking steps. Straight wire is formed into a helical coil, configured into a desired shape, secured to an insulated support rack, lugged with electrical connectors, and inspected for proper insulation and resistance characteristics. Commonly assigned U.S. Pat. No. 4,528,441 discloses different insulator designs and a scheme for manually securing the coil to the insulators. The scheme, however, was only suited for hand assembly and required manual manipulation for each attachment as the coil was wrapped around the support rack and the insulators deformed the coil to achieve attachment. Commonly assigned U.S. Pat. Nos. 4,807,488 and 4,827,602 disclose a method and apparatus for automatically installing a coiled heater element onto insulators. To date, however, there has been no equipment or apparatus which permits the efficient forming, moving, manipulating and checking to be done efficiently and automatically without damage to the assembly. In moving and manipulating coils by hand, there is a potential for misalignment of the nichrome coil during forming and handling which would change the desired resistance of the coil and cause the completed coil assembly to be rejected. No apparatus has been proposed that permits forming a length of coil cut to a desired length, and transferring the formed coil to a folding station for folding the coil to the desired configuration prior to transferring the folded coil to an automatic rack assembly fixture.
Coils have been formed with a desired diameter and pitch using wire of a known diameter to form an electrical coil of required resistance. However, as the formed coil is discharged from the coil winder, frictional forces, e.g. the friction of the coil moving across a support table, inhibit proper movement of the coil and cause the diameter or length to vary from desired values and cause the coil to compress whereby adjacent winding of the coil could contact each other and short out a portion of the coil. After the coil winder has formed a coil, the formed coil is manually moved to a folding station where an operator tries to center the coil length in the folding apparatus. After the coil is folded it is again manually moved to a coil/rack assembly station to fix the coil to the insulators of a rack.
Thus, there is a clear need for an apparatus and method for forming a coil of a desired length and transferring the formed coil to a first folding station without damaging the coil.